This invention relates generally to fittings, and more specifically to methods and apparatus for coupling a conduit to a fitting.
At least some known conduit fitting assemblies include a collar coupled to an end fitting. The end of the conduit end is received within a portion of the collar, and a portion of the end fitting is received within the conduit end. More specifically, the portion of the collar that includes the conduit end is then compressed radially inwardly such that the conduit end is compressed between the end fitting and the collar. When compressed, friction created between the collar and an outer surface of the conduit end, and friction created between an inner surface of the conduit end and the end fitting retains the conduit end within the collar.
The reliability of the conduit fitting assembly may vary over the life-cycle of the assembly based on the manufacturing tolerances of the conduit, collar, and end fitting. Dimensional departure from pre-established critical tolerances of the conduit, end fitting, collar, and the conduit fitting assembly may independently, or in aggregate, affect the outcome of quality testing. Accordingly, at least some known specification regulating bodies use qualification, sampling and periodic testing to verify manufacturing processes remain stable during manufacture. However, qualification, sampling, and periodic testing are typically only initiated at the beginning and end of manufacturing lots, and are usually destructive.
At least some known methods for testing a conduit fitting assembly include measuring an outer diameter of a compressed collar and an inner diameter of an end fitting to determine whether the assembly is acceptable. The number of times the collar is compressed to generate an acceptable collar outer diameter and end fitting inner diameter is determined by an operator, and may include more than one compression. However, correlation between the critical elements of the compression process, the tolerance stackup of critical characteristics of the collar, end fitting, conduit, and conduit fitting assembly as a whole, nor any performance or reliability criteria has been proven. Rather, only a general pass/fail of post-production sampling or periodic testing identifies whether the compression process and the critical tolerances for the end fitting, collar, conduit, and conduit fitting assembly are acceptable.